     (validate-concept concept)
     (let [{:keys [concept-type concept-id revision-id]} concept
           concepts (:concepts this)
-          concept-map (get @concepts concept-type)
+          concept-map (get @concepts (concept-type-prefix concept-type))
           revisions (get concept-map concept-id [])]
       (when (and revision-id
                  (not= (count revisions) revision-id))

(defn- reset-database
  "Empty the database."
  [db]
  (swap! (:concepts db) empty))
        
;;; An in-memory implementation of the provider store
(defrecord InMemoryStore

  data/ConceptStore
  
  (get-concept-id
    [this concept-type provider-id native-id]
    ;; We don't use the native-id for the in-memory implementation.
    ;; Other implementatations may want to use it.
    (let [type-prefix (concept-type-prefix concept-type)
          seq-num (concept-id-seq)]
      (str type-prefix "-" provider-id "-" seq-num)))
  
  (get-concept
    [this concept-id, revision-id]
    
    )
  
  (get-concepts
    [this concept-id-revision-id-tuples])
